The sentence means:
“I didn’t know that I had been doing it incorrectly all this time. I’m going to try the correct method tonight.”
Breakdown
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“Didn’t realize” → “I didn’t know / I hadn’t noticed”
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“I’ve been doing it wrong” → “I have been doing it incorrectly”
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“the entire time” → “all this time / throughout the whole time”
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“Gonna” → casual spoken form of “going to”
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“try this tonight” → “I’m going to try this method/idea tonight”
Natural German translation
„Ich wusste gar nicht, dass ich das die ganze Zeit falsch gemacht habe! Ich werde das heute Abend ausprobieren.“
The tone is casual, surprised, and excited to try something new.
